Transparent polyester resins and articles therefrom

ABSTRACT

Compositions suitable for preparing transparent articles comprising an aromatic polyester resin selected from a copolyalkylene terephthalate containing from 3 to 15% by moles of units derived from isophtalic acid and/or a naphtalene dicarboxylic acid and a polyxylylene amide, preferably poly (m.xylylene adipamide), in which the polymide is dispersed in the polyester resin as domains with average numeral size of 30 to 200 nm. The compositions are obtained by premelt-mixing the polyester with a dianhydride of a tetracarboxylic acid prior mixing the polyxylylene amide using melt viscosity ration between the polyester resin and the polyxylylene amide higher that 1.5:1, preferably from 3:1 to 8:1.

[0001] The present invention relates to compositions comprising anaromatic polyester resin and a polyxylylene amide having improvedtransparency characteristics and to the articles, in particular filmsand beverage containers, produced therefrom.

[0002] Particularly, the invention relates to blends of polyester resinsselected from polyalkylene terephthalates and copolyalkyleneterephthalates containing monomeric units derived from isophthalic acidand/or naphthalene dicarboxylic acids, with poly (m.xylylene adipamide)(poly-MXD-6).

TECHNICAL BACKGROUND

[0003] Aromatic polyester resins have excellent mechanical properties;however, their barrier properties to gases such as CO₂ and oxygen arenot sufficiently high. The barrier properties can be improved by mixingthe polyester resin, in the molten state, with a polyxylylene amide,particularly poly-MXD-6, used in quantity of about 5 to 30% by weight.

[0004] The barrier properties with respect to oxygen and CO₂ are furtherincreased if the composition comprising the polyester resin and thepolyxylylene amide is prepared by pre-mixing the polyester resin, in themolten state, with a dianhydride of a tetracarboxylic acid, particularlypyromellitic dianhydride (PMDA), and subsequently adding and mixing thepolyamide with the molten polyester resin (EP-A-964031).

[0005] The addition of the polyxylylene amide either to the polyesterresin premixed with the dianhydride or not containing the dianhydride,has the effect of reducing the transparency of the obtained articles.

[0006] The reduction in trasparency increases with the increase of thequantity of polyamide and of its molecular weight (WO-A-93/20147).Average numeral molecular weights of less than 15000 and amounts ofpolyamide less than 2 wt % are needed to limit the increase of opacity.

[0007] A need therefore exists of. providing polyester resins added withsignificant quantities of polyxylylene amide, which combine satisfactorybarrier properties to oxygen and CO₂ with high transparency and colourcharacteristics.

DESCRIPTION OF THE INVENTION

[0008] It has unexpectedly been found that it is possible to improve thetransparency and colour characteristics of aromatic polyester resinscontaining a polyxylylene amide in quantity from 1 to 30 wt % relativeto the polyester resin, if the polyamide is dispersed in the polyestermatrix in domains having average numeral size from 30 to 200 nm. Theabove fine dispersion is obtained by melt-mixing the polyester premixedwith a dianydride of a tetracarboxylic acid with the polyamide, providedthat the polyester is a copolyalkylene terephthalate (COPET) containingfrom 3 to 15% by mols or more of isophthalic acid units and/ornaphthalene dicarboxylic acid units, and that the melt viscosity ratiobetween the copolyalkylene terephthalate and the polyamide is higherthan 1.5:1.

[0009] The preferred polyamide is poly-MXD-6 which is preferably used inamounts of 1 to 15 wt % relative to the polyester resin.

[0010] Poly-MXD-6 in which all or part of the units derived from adipicacid are replaced by units deriving from dicarboxylic acids with 6-22carbon atoms other than adipic acid, such as for example suberic,azelaic and dodecanoic acids may also be used.

[0011] The mixing of the polyester resin, (pre melt-mixed with thedianhydride), and the polyxylylene amide is carried out in extruderunder conditions of temperature and shear forces such as to ensure afine and stable dispersion of the polyamide in the polyester matrix.Preferably, the extruded pellets are reextruded.

[0012] Shear rates higher than 100 s⁻¹ are used when melt-mixing thepolyamide.

[0013] The melt viscosity ratio of the polyester to the polyamide,evaluated at 280° C. and at shear rate of 100 s⁻¹, preferably is from3:1 to 8:1.

[0014] The domains of the polyxylilene amide dispersed in the polyestermatrix, preferably poly MXD-6, have an average numeral size generallyless than 100 nm (SEM determination on cast-film).

[0015] The distribution of the polyxylilene amide domains is such thatmore than 80% of the same have size from 80 to 110 nm and averagenumeral size fro 80 to 100 nm. Since the dispersed domains aresubstantially spheriform, the size is referred to the diameter.

[0016] The average numeral molecular weight of the polyxylylene amidepreferably is lower that 16000.

[0017] The relative viscosity conveniently ranges from 1.8 to 2.2.Polyxylilene amides with crystallization rates similar to that of thepolyester resin are preferred.

[0018] Concentrates in polyester of poly MXD-6 containing from 10 to 30%by weight of the.polyamide can also be used.

[0019] Dianhydride of the aromatic tetracarboxylic acids are preferred;pyromellitic dianhydride (PMDA) is the preferred dianhydride. Thedianhydride of 2,2 bis-(2,4 dicarboxy) ether and of 3,3′,4,4′-benzophenone tetracarboxylic acid are:examples of other suitablearomatic anhydrides.

[0020] The dianhidrides are used in quantity from 0.01 to 3%, preferably0.01 to 0.4% by weight relative to the polyester resin.

[0021] The aromatic polyester resins are produced according to knownmethods by polycondensation of an aromatic dicarboxylic acid, or bytransestenrification of the lower dialkyl esters of said acids, with adiol with 2-12 carbon atoms.

[0022] Ethylene terephthalate copolymers containing from 3 to 7% by molsof units derived from isophthalic acid and/or a-naphthalene dicarboxylicacid, particularly 2,6-naphthalene dicarboxylic acid, are preferred.

[0023] The intrinsic viscosity of the COPET resin is preferablycomprised from 0.6 to 0.9 dl/g.

[0024] The haze of a cast film 0.5 mm thick is not higher than 3%,generally is 1-2%. The color parameter of the pellets is from 0.56 to3.57.

[0025] The compositions are usable in many applications, in particularfor the preparation of transparent and having gas barrier propertiesfilms bioriented or not obtained by cast extrusion or by blowing usingthe single-bubble or the double-bubble technique or by the tenter-frametechnique and beverage bottles produced by injection stretchblow-molding.

Analytical Measurements

[0026] The intrinsic viscosity of the polyester resin has beendetermined in solution (approxymately 0.5 g of resin) in a 60/40 byweight mixture of phenol and 2,2-tetrachloroethane at 25° C., inaccordance with ASTM 4603-86.

[0027] The relative viscosity of the polyxylylene amide was determinedat 25° C. in a solution of 1 g polyamide in 100 ml sufphuric acid at aconcentration of 96 wt %.

[0028] The melt viscosity of the resins was determined at 280° C. at ashear rate of 100 sec⁻¹.

[0029] The haze measurement was determined according to ASTM D 1300.

[0030] The following examples are provided by way of non-limitingillustration of the invention.

[0031] The poly MXD6 used in the examples belonging to the invention wasprepared by melt-polycondensation according to known methods. Thepolyamide was dried prior being fed into the extruder.

COMPARISON EXAMPLE 1

[0032] Copolyethylene terephthalate (COPET) containing 2.2% by weight ofunits from isophthalic acid and mixed in the molten state in extruderwith 0.1% by wight of PMDA was mixed in extruder with 10% by weight ofcommercial MXD-6 grade 6007, commercialized by Mitsubishi Gas havingrelative viscosity of 2.7.

[0033] The melt viscosity ratio between COPET and MXD6 was 1.25:1.

[0034] The extrusion ,conditions were: cylinder temperature 280° C.,extrusion-head temperature 275° C. The used extruder was an intermeshingtwin extruder with diameter of the screws of 30 cm and L/D of 20; therate of extrusion was 10 kg/h.

[0035] The chips produced had a b* colour parameter of 0.88.

[0036] The chips were crystallized at 140° C. in a stream of nitrogenand then extruded to form a cast film 100 mm wide and 0.5 mm thick(cylinder temperature 280° C., temperature of 275° C. at the extrusionflat-head).

[0037] The haze of the film produced was 4%; the SEM photograph showedthat MXD6 was. dispersed in domains having average, numeral size of 220nm (FIG. 1 reproduces in graphic form the size and the distribution ofthe dispersed MXD6 particles shown in the photograph).

COMPARISON EXAMPLE 2

[0038] Comparison example 1 was repeated with the only difference thatthe COPET contained 5% of isophthalic unis. The I.V. was 0.76 dl/g.

[0039] The melt viscosity ratio between COPET and MXD6 was 1.1:1. Thehaze of the cast film was 3.5%

EXAMPLE 1

[0040] Comparison Example 1 was repeated with the only difference thatwas used a poly MXD6 having relative viscosity of 2.1. The meltviscosity ratio of PET to MXD6 was 4:1.

[0041] The haze value of the cast film was 2.3%. The polyamide resultedto be dispersed in the polyester matrix in spheriform domains of 100 nmof average diameter (SEM determination on the the fracture surface of asmall bar obtained by injection molding and treated with formic acid toextract the polyamide).

[0042] The size and the distribution of the particles are reported inFIG. 2.

EXAMPLE 2

[0043] Example 1 was repeated with the only difference that the polyMXD-6 had a relative viscosity of 2.0. The cast-film had haze of 1.8%.

EXAMPLE 3

[0044] Example 2 was repeated with the only difference that PMDA wasused in amount of 0,4% on COPET. The cast-film had haze of 1.9%. The SEMdetermination of the microstructure showded that the polyamide wasdispersed in spheriform domains having an average numeral diameter al80-100 nm; more that 80% of the particles had a diameter from 80 to 110nm and average numeral diameter from 80 to 100 nm.

COMPARISON EXAMPLE 3

[0045] Comparison example 1 was repeated with the only difference thatthe COPET was not added with PMDA. The cast film had haze of 3.4%. Thesize of the poly MXD-6 domains was greater than 200 nm.

EXAMPLE 4

[0046] Beverage bottles of 1.5 l capacity were prepared by injectionstretch blow-molding from the composition of EXAMPLE 3 and of COMPARISONEXAMPLE 1. The bottles produced from the composition of EXAMPLE 3appeared significantly more transparent than those of COMPARISONEXAMPLE 1. The haze of bottles of EXAMPLE 3 was 2-2.5%; that of bottlesof COMPARISON EXAMPLE 1 of 3.2-3.4%.

1. A composition for preparing articles having high transparencycomprising an aromatic polyester resin and a polyamide, in which thearomatic polyester resin is selected from the copolyalkyleneterephthalates containing from 3 to 15% by mols of units derived fromisophthalic acid and/or napthalene dicarboxylic acids and the polyamideis dispersed in the aromatic polyester resin matrix as domains havingaverage numeral size from 30 to 200 nm.
 2. A composition according toclaim 1, in which the polyamide is poly (m. xylylene adipamide) used inamount of 1 to 15% by weight relative to the polyester resin.
 3. Acomposition according to claim 2 wherein the aromatic polyester resin isselected from copolyalkylene terephthalates containing from 4 to 7% bymoles of units derived from isophthalic acid and/or naphthalenedicarboxylic acids.
 4. An article having haze less than 3% obtained fromthe composition according to claim
 1. 5. A film or container having hazeless than 3% obtained from the composition according to claim 1 and inwhich the polyamide is dispersed in the polyester matrix in domainshaving average numeral size of 30 to 200 nm.
 6. A film or containeraccording to claim 5, in which the polyamide is poly(m.xylylenadipamide).
 7. A composition according to claim 1 wherein thedomains have an average numeral size of 80 to 100 nm, and wherein morethan 80% of the domains have a size of 80 to 110 nm.
 8. A compositionaccording to claim 7, in which the polyxylylene amide is poly (m.xylylene adipamide) used in amount of 1 to 15% by weight relative to thepolyester resin.
 9. A composition according to claim 8 wherein thepolyester resin is selected from copolyalkylene terephthalatescontaining from 4 to 7% by moles of units derived from isophthalic acidand/or naphthalene dicarboxylic acids.
 10. An article having haze lessthan 3% obtained from the composition according to claim
 7. 11. A filmor container having haze less than 3% obtained from the compositionaccording to claim 7 and in which the polyamide is dispersed in thepolyester matrix in domains having average numeral size of 80 to 100 nm,wherein more than 80% of the domains have size of 80 to 100 nm.
 12. Afilm or container according to claim 11, in which the polyamide is poly(m.xylylenadipamide).
 13. A process for preparing compositions accordingto claim 1 in which a polyalkylene terephthalate containing from 3 to15% by mols of units derived from isophthalic acid and/or naphthalenedicarboxylic acids is melt-mixed with a dianhydride of a tetracarboxylicacid in amount from 0.02 to 0.4 wt % on the polyester resin andsubsequently is mixed with the polyamide having melt viscosity referredto that of the polyalkylene terephthalate in a ratio of 1:3 to 1:8. 14.A composition according to claim 1 wherein the aromatic polyester resinis selected from copolyalkylene terephthalates containing from 4 to 7%by moles of units derived from isophthalic acid and/or naphthalenedicarboxylic acids.
 15. A composition according to claim 1 in which theratio of the melt viscosity of the polyamide to the melt viscosity ofthe polyalkylene terephthalate is 1:3 to 1:8.
 16. A compositionaccording to claim 2 in which the ratio of the melt viscosity of thepoly(m.xylyleneadipamide) to the melt viscosity of the polyalkyleneterephthalate is 1:3 to 1:8.
 17. A composition according to claim 3 inwhich the ratio of the melt viscosity of the poly(m.xylyleneadipamide)to the melt viscosity of the polyalkylene terephthalate is 1:3 to 1:8.18. A composition according to claim 7 in which the ratio of the meltviscosity of the polyamide to the melt viscosity of the polyalkyleneterephthalate is 1:3 to 1:8.
 19. An article according to claim 11 inwhich the ratio of the melt viscosity of the polyamide to the meltviscosity of the polyalkylene terephthalate is 1:3 to 1:8.
 20. Acomposition as specified in claim 1 wherein the polyamide is apolyxylylene amide.